1. Field of the Invention
This invention relates in general to a method of preventing cellular telephone fraud, and more specifically to a method of preventing cellular phone fraud using a pre-authorization technique for subscriber roaming privileges.
2. Description of Related Art
Cellular telephones combine the mobility of the radio link and the world-wide land telephone network to provide a communication link to any other telephone in the world. However, as cellular phones have become more prevalent throughout the country, fraud has become a major problem. Cellular fraud robs service providers of hundreds of millions of dollars every year. Like all crimes, there are several varieties of cellular fraud, including "cloning." Cloning fraud, which occurs when a legitimate subscriber's mobile identification number/electronic serial number (MIN/ESN) combination is used for illegal purposes, is among the most sophisticated and difficult forms of fraud to prevent. Often, the pirate will use simple electronic devices to "capture" the legitimate MIN/ESN combination during its transmission by radio frequency (RF). In these cases, the legitimate subscriber often does not know fraud is being committed with his or her MIN/ESN combination until they receive their bill. This is currently the most popular method of gaining illegal access to a cellular system, because the legitimacy of the stolen MIN/ESN combinations makes cloning difficult to catch.
Often, cloning fraud occurs outside of the home area of the subscriber. Once the MIN/ESN information has been cloned, the MIN/ESN combination is valid for access to the cellular telephone system anywhere. Roamer fraud is committed by a local thief using a MIN/ESN imported from another service area, and thus not representing a true roaming subscriber. The exploited MIN/ESN is usually gathered through the use of a MIN/ESN reader in a home service area for the cellular phone.
There are certain steps that can be taken to prevent cloning fraud. For example, U.S. Pat. No. 5,249,230 discloses a "challenge-response" system, wherein the cellular system "challenges" a cellular phone subscriber prior to granting access. The subscriber must manually "respond" to the challenge by entering a Personal Identification Number (PIN) or other code that is then verified against a centralized database maintained by the cellular system. However, this method is not attractive to most subscribers since it requires additional work and inconvenience.
In another example, U.S. Pat. No. 5,239,294 discloses a technique that encrypts a PIN that is permanently programmed into the cellular phone, wherein the PIN is automatically transmitted to the cellular network during call setup. However, this method is expensive to implement, and is still subject to cloning, since the cloner need not discriminate between encrypted and unencrypted PINs to merely repeat a sequence of numbers observed being transmitting to the cellular system.
Call pattern monitoring is another method used to prevent cellular phone fraud. This method works because most subscribers call only a specific set of phone numbers. When a call for a subscriber falls outside of that usual group, a challenge-response action can be initiated by the service provider. However, for new subscribers who have no previous calling history, or for subscribers who have a wide range of calling patterns, this method is ineffective.
It can be seen, then, that there is a need for more effective techniques for preventing cellular phone fraud. Furthermore, such techniques must be easy and inexpensive to implement, and must not put unacceptable demands on subscribers.